1. Light a grill. Arrange the potato pierogi on a large baking sheet and brush generously with olive oil. In a small bowl, mix the chopped tomato with the sliced onion and jalapeño. Season with salt and pepper.
2. Brush the shiitake mushroom caps with olive oil and season with salt and pepper. Grill the mushroom caps over a medium-hot fire until tender and nicely browned, about 4 minutes per side. Thinly slice the mushrooms and transfer to a bowl. Toss the mushrooms with the scallions.
3. Grill the pierogi over a medium-hot fire until they are browned and crisp, about 2 minutes per side. Transfer the pierogis to a large platter and spread with the sour cream. Spoon the mushroom topping over half of the pierogi and spoon the tomato salsa over the rest. Serve hot.
Notes: If you use frozen pierogi that are not precooked, you must boil them first, then drain and let cool completely before grilling. BEER The creamy, earthy and spicy elements in these crostini call for a bright, golden lager with plenty of flavor to match. Try the classic Pilsner Urquell or the smooth and strong Polish Piast.